Y.F. Qi

Study on the overall heat transfer coefficient for the tube-in-tube heat exchanger used in mixed-gases coolers

In this paper, an experimental set up is established to investigate the behavior of the heat exchanger with multi-components mixtures based on a real mixture refrigeration system. Two tube-in-tube heat exchangers with different configurations are tested extensively with different mixtures operating at three typical temperature ranges, such as 80 K–100 K, 120 K–150 K, and 180 K–200 K temperature ranges. The two heat exchangers are fabricated specially to be able to measure the temperatures and pressures distributions. With the measurement of the mixture compositions, temperatures, and pressures, the thermodynamic and hydraulic behaviors of the two heat exchangers are studied extensively. Finally, the heat transfer characteristics are obtained, which is useful in future design of the mixture refrigeration system.

Research on the change of mixture compositions in mixed-refrigerant Joule-Thomson cryocoolers

An experimental system is developed to investigate the dynamic characteristics of the mixture composition variations in the closed throttling refrigeration cycle. The experimental results show that the mixture compositions vary at different operating periods of the cycle. The maximum change of the compositions is up to 6% for different operating periods. The unevenness of the mixture compositions at different positions of the system may be up to 12%, or even more. The experimental results will be helpful in the modification of the existing simulation model of the mixture refrigeration cycle as well as the fabrication of mixture coolers.

A new type mixture refrigeration auto-cascade cycle with partial condensation and separation reflux exchanger and its preliminary experimental test

A new type of mixture refrigeration cycle with reflux exchanger is presented in this paper. In this cycle, a new type of L-V separator with inner heat and mass transfer is employed to replace the combination of conventional L-V separator or complicated rectifier and succeeding heat exchanger used in traditional auto-cascade cycle or Kleemenko cycle. A prototype is developed based on this refrigeration cycle. The thermodynamic performance is discussed as well as some other specifications such as cost, reliability, etc. The experimental results show that this prototype can reach 74 W at 135 K and 265 W at 171 K with a nominal input power of 1.5 HP.

Study of a Vortex Tube by Analogy with a Heat Exchanger

Based on the models of Scheper, Lewins, and Bejan, a new model has been established to study the influence of the cold mass flow fraction on the temperature separation effect in a vortex tube. The model is based on making an analogy between the vortex tube and a counterflow heat exchanger. The results show the model can accurately explain the correlation of cold mass flow fraction to the temperature separation effect.

Thermodynamic Prediction of the Vortex Tube Applied to a Mixed-Refrigerant Auto-Cascade J-T Cycle

A new hybrid refrigeration cycle of the Mixed-refrigerant Auto-Cascade J-T cycle combined with a vortex tube is introduced. This cycle, which holds the advantage of a mixed refrigerant Auto-Cascade J-T cycle and the vortex tube, is expected to achieve a temperature lower than 65 K. A thermodynamic model is used to investigate the vortex tube energy separation. The exergy method is applied to analyze the thermodynamic performance of each unit and the whole refrigeration cycle. A comparison is made between the Auto-Cascade J-T cycle and the new hybrid refrigeration cycle for the same conditions. The total exergy efficiency achieved in the new hybrid refrigeration cycle is 78.9% better than the Auto-Cascade J-T cycle. The results show that using the new type of compound refrigeration cycle can improve exergy efficiency of the whole cycle. It is completely possible to achieve a temperature lower than 65 K.

Further Development of the Mixture Refrigeration Cycle with a Dephlegmation Separator

Mixed gas refrigeration cycles with phase separators provide a wealth of configuration options for the design of the cycle. This paper focuses on the development of the cycle with a simplified dephlegmation separator. Both theoretical analysis and experimental investigation were carried out to optimize the refrigeration cycle configuration, including the arrangement of the heat exchangers, phase separator, mixer, etc. Particular attention is placed on the position of the mixer. Experimental results confirm the conclusions drawn from the thermodynamic analysis of the configuration of the dephlegmation cycle. A Carnot efficiency of 11.7% was achieved in an experimental test at 125 K with the cycle driven by an air-conditioning compressor with a nominal input power of 1.1 kW.

Experimental investigation on pool boiling heat transfer of pure refrigerants and binary mixtures

Publisher Summary This chapter measures heat transfer coefficients in nucleate boiling on a smooth flat surface for pure fluids of R-134a, propane, isobutane, and their binary mixtures at different pressure from 0.1 to 0.6 MPa. Special emphasis is laid on the question, how the influence of the heat flux and pressure on the heat transfer coefficient is predicted at different saturation pressures. Several pool boiling heat transfer correlations for pure refrigerants are compared, and a new correlation is proposed based on the experimental data. A wide range of heat flux and mixture concentrations is covered in the experiment. The influences of pressure and heat flux on the heat transfer coefficient for different pure fluids are studied. Isobutane and propane are used to make up binary mixtures. Compared to the pure components, binary mixtures show lower heat transfer coefficients. This reduction is more pronounced as heat flux is increased. More binary mixtures and ternary mixtures are investigated and new heat transfer correlations are developed according to the experimental data in future.

Dimensional analysis on multi-component mixed-refrigerants flow characteristics in adiabatic capillary tube

Publisher Summary This chapter charts the development of a dimensionless correlation to predict the mixed-refrigerants flow characteristics through adiabatic capillary tube. In multi-component mixed-refrigerants Joule-Thomson cryocooler, the refrigerants flow in the capillary tube is very complicated. Most design methods in the literatures were developed on a theoretical simulation of the two-phase flow through the tube with some simple assumptions such as homogenous two-phase flow and constant friction factor along the tube. Some correlations or methods were valid only for limited refrigerants. The process of refrigerant flow through the capillary tube is a flash process, in which the refrigerant flows at a high speed and changes from liquid to vapor-liquid blend. In practical consideration, main concern is the refrigerants flowing characteristics for matching the system to get the highest performance. Different from the correlations in the room-temperature refrigeration system, the pressure at the outlet of the capillary tube should be considered in correlation for mixed-refrigerants because the critical condition was not reached. According to the correlation, the primary factors that influence mixed-refrigerants flow characteristics in adiabatic capillary tube were obtained. The result can give a guide for system design.

Research on Adiabatic Capillary Tube Expansion Devices in Mixed-Refrigerant J-T Cryocoolers

This paper presents a study of capillary tubes used as expansion devices in mixed-refrigerant J-T cryocoolers. A numerical model is presented for predicting capillary tube performance with multicomponent refrigerants, and the results are compared with experimental data. Because of the multicomponent refrigerant used in the system, the flow characteristic is different from that in a household refrigerator or freezer. The experimental results are discussed, and the performance of the capillary is analyzed.